(i) Field of the Invention
This invention relates to a wireless communication system using a wireless LAN (wireless local area network), particularly to a wireless communication system based on IEEE802.11 which is a standard for a wireless LAN and Mobile IPv6 which is a next-generation Internet protocol.
(ii) Description of the Related Art
As a wireless communication system using a wireless LAN, a wireless communication system using Mobile IPv6 which is a next-generation Internet protocol has been becoming increasingly popular. The wireless communication system using Mobile IPv6 will be described with reference to FIG. 1. A wireless communication system shown in FIG. 1 comprises a plurality of subnetworks, i.e., a subnetwork 20 and a subnetwork 30 in this case, and a mobile node (MN) which is connectable to any of the subnetworks, i.e., an MN 10 in this case.
The subnetwork 20 comprises an access router (AR) 21 which handles routing of packet data and an access point (AP) 22 which is connected to the AR 21 so as to form a specific communicatable range (cell) 23 and perform wireless communication with the MN 10 which is present within the cell 23. The AR 21 is connected to an AR in each of subnetworks adjacent to the subnetwork 20. The subnetwork 30 has a similar constitution to that of the subnetwork 20.
In such a wireless communication system, the MN 10 present within the cell 23 can transmit or receive packet data by acquiring an IP address adapted to the subnetwork 20, i.e., a care of address, from the AR 21 via wireless communication with the AP 22. Thereby, packet data transmitted from a given transmitter to the MN 10 is passed to the MN 10 via the AR 21 and the AP 22 based on the care of address of the MN 10, while packet data transmitted from the MN 10 to a desired receiver is passed to the desired receiver via the AP 22 and the AR 21.
The wireless communication system using Mobile IPv6 shown in FIG. 1 provides wireless communication assuming that an MN moves from a range corresponding to a cell to a range corresponding to another cell. To implement wireless communication smoothly even if the MN makes such a movement, the wireless communication system using Mobile IPv6 employs a BETH (Bi-directional Edge Tunnel Handover) technique in particular among Fast Handover (FHO) Techniques. The BETH will be described with reference to an exemplary case where the MN 10 moves from a point A in the cell 23 to a point B in a cell 33.
Before the MN 10 moves from the point A to the point B, the AR 21 notifies the AR 31 that the MN 10 will move into the cell 33. Thereby, a tunnel or BET (Bi-directional Edge Tunnel) is established between the AR 21 and the AR 31.
In order for the MN 10 to connect to the subnetwork 30 and implement wireless communication after moving into the cell 33, it must basically newly acquire a care of address adapted to the subnetwork 30. However, since the BET is established between the AR 21 and the AR 31, packet data transmitted to the MN 10 is passed from the AR 21 to the AR 31 via the BET first and then passed to the MN 10 via the AP 32, even before the MN 10 acquires the new care of address. Meanwhile, packet data transmitted from the MN 10 to a desired receiver is passed to the AR 31 via the AP 32 first, then passed from the AR 31 to the AR 21 via the BET, and then passed to the desired receiver.
Then, after the MN 10 acquires the new care of address adapted to the subnetwork 30 from the AR 31 via wireless communication with the AP 32, it transmits or receives packet data by use of the new care of address.
In such BETH as described above, it is intended that transmission and reception of packet data can be implemented smoothly even when the MN 10 has moved from the cell 23 to the cell 33.
However, the above wireless communication system using Mobile IPv6 has the following problem.
That is, firstly, in the wireless communication system shown in FIG. 1, Mobile IPv6 is used as a protocol between the MN and the AR, and IEEE802.11 which is a standard associated with a wireless LAN is generally used as a protocol between the MN and the AP.
In the Mobile IPv6 specification, it is described with respect to handover that a network or AR indicates an MN a subnetwork for handover. That is, network-based handover is supported in Mobile IPv6. Meanwhile, it is described in the IEEE802.11 specification that an MN determines a subnetwork for handover by itself. That is, MN-based handover is supported in IEEE802.11.
Therefore, when IEEE802.11 is used between the MN and the AP in the wireless communication system shown in FIG. 1 in the above example, the MN 10 does handover to the subnetwork 30 that it has determined by itself, without providing any notification to the AR 21 of the subnetwork 20 to which the MN 10 has been connected. As a result, since the AR 21 of the subnetwork 20 cannot know that the MN 10 does handover to the subnetwork 30, the AR 21 cannot establish a BET between the AR 31 and itself.
To solve the problem, it is conceivable that the AP notifies the MN of a subnetwork for handover by itself. However, as described above, IEEE802.11 is used between the MN and the AP, and a signal used by the AP to give such a notification to the MN is not defined in the IEEE802.11. Further, the specification of the IEEE802.11 has already been set in 1,999 and spread all over the world. Accordingly, it is impossible to alter the contents of the specification of the IEEE802.11 at the present time.